Imperial College London

Emeritus ProfessorKenMacLeod

Faculty of MedicineNational Heart & Lung Institute

Emeritus Professor of Cardiac Physiology
 
 
 
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Contact

 

+44 (0)20 7594 2734k.t.macleod

 
 
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Assistant

 

Miss Natasha Richmond +44 (0)20 7594 6457

 
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Location

 

336ICTEM buildingHammersmith Campus

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Summary

 

Publications

Publication Type
Year
to

174 results found

MacLeod K, 2023, Sex-related differences in biology - ignore them at your peril, The Journal of Physiology, Vol: 601, Pages: 3983-3984, ISSN: 0022-3751

Journal article

Dark N, Cosson M-V, Tsansizi LI, Owen TJ, Ferraro E, Francis AJ, Tsai S, Bouissou C, Weston A, Collinson L, Abi-Gerges N, Miller PE, MacLeod KT, Ehler E, Mitter R, Harding SE, Smith JC, Bernardo ASet al., 2023, Generation of left ventricle-like cardiomyocytes with improved structural, functional, and metabolic maturity from human pluripotent stem cells, Cell Reports: Methods, Vol: 3, ISSN: 2667-2375

Decreased left ventricle (LV) function caused by genetic mutations or injury often leads to debilitating and fatal cardiovascular disease. LV cardiomyocytes are, therefore, a potentially valuable therapeutical target. Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are neither homogeneous nor functionally mature, which reduces their utility. Here, we exploit cardiac development knowledge to instruct differentiation of hPSCs specifically toward LV cardiomyocytes. Correct mesoderm patterning and retinoic acid pathway blocking are essential to generate near-homogenous LV-specific hPSC-CMs (hPSC-LV-CMs). These cells transit via first heart field progenitors and display typical ventricular action potentials. Importantly, hPSC-LV-CMs exhibit increased metabolism, reduced proliferation, and improved cytoarchitecture and functional maturity compared with age-matched cardiomyocytes generated using the standard WNT-ON/WNT-OFF protocol. Similarly, engineered heart tissues made from hPSC-LV-CMs are better organized, produce higher force, and beat more slowly but can be paced to physiological levels. Together, we show that functionally matured hPSC-LV-CMs can be obtained rapidly without exposure to current maturation regimes.

Journal article

MacLeod KT, 2023, Changes in cellular Ca2+ and Na+ regulation during the progression towards heart failure, The Journal of Physiology, Vol: 601, Pages: 905-921, ISSN: 0022-3751

In adapting to disease and loss of tissue, the heart shows great phenotypic plasticity that involves changes to its structure, composition and electrophysiology. Together with parallel whole body cardiovascular adaptations, the initial decline in cardiac function resulting from the insult is compensated. However, in the long term, the heart muscle begins to fail and patients with this condition have a very poor prognosis, with many dying from disturbances of rhythm. The surviving myocytes of these hearts gain Na+, which is positively inotropic because of alterations to Ca2+ fluxes mediated by the Na+/Ca2+ exchange, but compromises Ca2+-dependent energy metabolism in mitochondria. Uptake of Ca2+ into the sarcoplasmic reticulum (SR) is reduced because of diminished function of SR Ca2+ ATPases. The result of increased Ca2+ influx and reduced SR Ca2+ uptake is an increase in the diastolic cytosolic Ca2+ concentration, which promotes spontaneous SR Ca2+ release and induces delayed afterdepolarisations. Action potential duration prolongs because of increased late Na+ current and changes in expression and function of other ion channels and transporters increasing the probability of the formation of early afterdepolarisations. There is a reduction in T-tubule density and so the normal spatial arrangements required for efficient excitation–contraction coupling are compromised and lead to temporal delays in Ca2+ release from the SR. Therefore, the structural and electrophysiological responses that occur to provide compensation do so at the expense of (1) increasing the likelihood of arrhythmogenesis; (2) activating hypertrophic, apoptotic and Ca2+ signalling pathways; and (3) decreasing the efficiency of SR Ca2+ release.

Journal article

Dvinskikh L, Sparks H, Brito L, MacLeod K, Harding S, Dunsby Cet al., 2023, Remote-refocusing light-sheet fluorescence microscopy enables 3D imaging of electromechanical coupling of hiPSC-derived and adult cardiomyocytes in co-culture, Scientific Reports, Vol: 13, Pages: 1-14, ISSN: 2045-2322

Improving cardiac function through stem-cell regenerative therapy requires functional and structural integration of the transplanted cells with the host tissue. Visualizing the electromechanical interaction between native and graft cells necessitates 3D imaging with high spatio-temporal resolution and low photo-toxicity. A custom light-sheet fluorescence microscope was used for volumetric imaging of calcium dynamics in co-cultures of adult rat left ventricle cardiomyocytes and human induced pluripotent stem cell-derived cardiomyocytes. Aberration-free remote refocus of the detection plane synchronously to the scanning of the light sheet along the detection axis enabled fast dual-channel 3D imaging at subcellular resolution without mechanical sample disturbance at up to 8 Hz over a ∼300 µm × 40 µm × 50 µm volume. The two cell types were found to undergo electrically stimulated and spontaneous synchronized calcium transients and contraction. Electromechanical coupling improved with co-culture duration, with 50% of adult-CM coupled after 24 h of co-culture, compared to 19% after 4 h (p = 0.0305). Immobilization with para-nitroblebbistatin did not prevent calcium transient synchronization, with 35% and 36% adult-CM coupled in control and treated samples respectively (p = 0.91), indicating that electrical coupling can be maintained independently of mechanotransduction.

Journal article

Dvinskikh L, Sparks H, MacLeod K, Dunsby Cet al., 2023, High-speed 2D light-sheet fluorescence microscopy enables quantification of spatially varying calcium dynamics in ventricular cardiomyocytes, Frontiers in Physiology, Vol: 14, Pages: 1-14, ISSN: 1664-042X

Introduction: Reduced synchrony of calcium release and t-tubule structure organization in individual cardiomyocytes has been linked to loss of contractile strength and arrhythmia. Compared to confocal scanning techniques widely used for imaging calcium dynamics in cardiac muscle cells, light-sheet fluorescence microscopy enables fast acquisition of a 2D plane in the sample with low phototoxicity.Methods: A custom light-sheet fluorescence microscope was used to achieve dual-channel 2D timelapse imaging of calcium and the sarcolemma, enabling calcium sparks and transients in left and right ventricle cardiomyocytes to be correlated with the cell microstructure. Imaging electrically stimulated dual-labelled cardiomyocytes immobilized with para-nitroblebbistatin, a non-phototoxic, low fluorescence contraction uncoupler, with sub-micron resolution at 395 fps over a 38 μm × 170 µm FOV allowed characterization of calcium spark morphology and 2D mapping of the calcium transient time-to-half-maximum across the cell.Results: Blinded analysis of the data revealed sparks with greater amplitude in left ventricle myocytes. The time for the calcium transient to reach half-maximum amplitude in the central part of the cell was found to be, on average, 2 ms shorter than at the cell ends. Sparks co-localized with t-tubules were found to have significantly longer duration, larger area and spark mass than those further away from t-tubules.Conclusion: The high spatiotemporal resolution of the microscope and automated image-analysis enabled detailed 2D mapping and quantification of calcium dynamics of n = 60 myocytes, with the findings demonstrating multi-level spatial variation of calcium dynamics across the cell, supporting the dependence of synchrony and characteristics of calcium release on the underlying t-tubule structure.

Journal article

Hong W, Wright T, Sparks H, Dvinskikh L, MacLeod K, Paterson C, Dunsby Cet al., 2022, Adaptive light-sheet fluorescence microscopy with a deformable mirror for video-rate volumetric imaging, Applied Physics Letters, Vol: 121, Pages: 1-7, ISSN: 0003-6951

Light-sheet fluorescence microscopy (LSFM) achieves optically sectioned imaging with the relatively low photobleaching and phototoxic effect. To achieve high-speed volumetric LSFM imaging without perturbing the sample, it is necessary to use some form of remote refocusing in the detection beam path. Previous work used electrically tunable lenses, tunable acoustic gradient index of refraction lenses, or the remote-refocusing approach of Botcherby et al. [Opt. Lett. 32(14), 2007 (2007)] to achieve remote refocusing. However, these approaches generally only provide low-order defocus correction, which is not compatible with higher-NA objectives that require higher order defocus corrections or reduce the optical throughput. In order to simultaneously achieve high-speed remote refocusing and correct system aberrations, we employ a deformable mirror in the detection path that is capable of providing higher orders of defocus and aberration correction in an optical system with an NA of 0.72–0.75. We demonstrate high-speed volumetric imaging at 26.3 volumes per second and 35 frames per volume for a defocus range of −50 to 50 μm.

Journal article

Francis A, Firth J, Sanchez-Alonso J, Gorelik J, MacLeod Ket al., 2022, GPER limits adverse changes to Ca2+ signalling and arrhythmogenic activity in ovariectomised guinea pig cardiomyocytes, Frontiers in Physiology, Vol: 13, ISSN: 1664-042X

Background: The increased risk of post-menopausal women developing abnormalities of heart function emphasises the requirement to understand the effect of declining oestrogen levels on cardiac electrophysiology and structure, and investigate possible therapeutic targets, namely the G protein-coupled oestrogen receptor 1 (GPER).Methods: Female guinea pigs underwent sham or ovariectomy (OVx) surgeries. Cardiomyocytes were isolated 150-days post-operatively. Membrane structure was assessed using di-8-ANEPPs staining and scanning ion conductance microscopy. Imunnohistochemistry (IHC) determined the localisation of oestrogen receptors. The effect of GPER activation on excitation-contraction coupling mechanisms were assessed using electrophysiological and fluorescence techniques. Downstream signalling proteins were investigated by western blot.Results: IHC staining confirmed the presence of nuclear oestrogen receptors and GPER, the latter prominently localised to the peri-nuclear region and having a clear striated pattern elsewhere in the cells. Following OVx, GPER expression increased and its activation reduced Ca2+ transient amplitude (by 40%) and sarcomere shortening (by 32%). In these cells, GPER activation reduced abnormal spontaneous Ca2+ activity, shortened action potential duration and limited drug-induced early after-depolarisation formation.Conclusion: In an animal species with comparable steroidogenesis and cardiac physiology to humans, we show the expression and localisation of all three oestrogen receptors in cardiac myocytes. We found that following oestrogen withdrawal, GPER expression increased and its activation limited arrhythmogenic behaviours in this low oestrogen state, indicating a potential cardioprotective role of this receptor in post-menopausal women.

Journal article

Wang BX, Kane C, Nicastro L, King O, Kit-Anan W, Downing B, Deidda G, Couch LS, Pinali C, Mitraki A, MacLeod KT, Terracciano CMet al., 2022, Integrins Increase Sarcoplasmic Reticulum Activity for Excitation-Contraction Coupling in Human Stem Cell-Derived Cardiomyocytes, INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES, Vol: 23

Journal article

Bannister ML, MacLeod KT, George CH, 2022, Moving in the right direction: elucidating the mechanisms of interaction between flecainide and the cardiac ryanodine receptor, BRITISH JOURNAL OF PHARMACOLOGY, Vol: 179, Pages: 2558-2563, ISSN: 0007-1188

Journal article

Hesketh LM, Sikkel MB, Mahoney-Sanchez L, Mazzacuva F, Chowdhury RA, Tzortzis KN, Firth J, Winter J, MacLeod KT, Ogrodzinski S, Wilder CDE, Patterson LH, Peters NS, Curtis MJet al., 2022, OCT2013, an ischaemia-activated antiarrhythmic prodrug, devoid of the systemic side effects of lidocaine, British Journal of Pharmacology, Vol: 179, Pages: 2037-2053, ISSN: 0007-1188

BACKGROUND AND PURPOSE: Sudden cardiac death (SCD) caused by acute myocardial ischaemia and ventricular fibrillation (VF) is an unmet therapeutic need. Lidocaine suppresses ischaemia-induced VF, but utility is limited by side effects and a narrow therapeutic index. Here we characterise OCT2013, a putative ischaemia-activated prodrug of lidocaine. EXPERIMENTAL APPROACH: The rat Langendorff-perfused isolated heart, anaesthetised rat and rat ventricular myocyte preparations were utilised in a series of blinded and randomised studies to investigate the antiarrhythmic effectiveness, adverse effects and mechanism of action of OCT2013, compared with lidocaine. KEY RESULTS: In isolated hearts, OCT2013 and lidocaine prevented ischaemia-induced VF equi-effectively, but OCT2013 did not share lidocaine's adverse effects (PR widening, bradycardia and negative inotropy). In anesthetised rats, i.v. OCT2013 and lidocaine suppressed VF and increased survival equi-effectively; OCT2013 had no effect on cardiac output even at 64 mg.kg-1 i.v., whereas lidocaine reduced it even at 1 mg.kg-1 . In adult rat ventricular myocytes, OCT2013 had no effect on Ca2+ handling whereas lidocaine impaired it. In paced isolated hearts, lidocaine caused rate-dependent conduction slowing and block, whereas OCT2013 was inactive. However, during regional ischaemia, OCT2013 and lidocaine equi-effectively hastened conduction block. Chromatography and mass spectrometry analysis revealed that OCT2013, detectable in normoxic OCT2013-perfused hearts, became undetectable during global ischaemia, with lidocaine becoming detectable. CONCLUSIONS AND IMPLICATIONS: OCT2013 is inactive but is bioreduced locally in ischaemic myocardium to lidocaine, acting as an ischaemia-activated and ischaemia-selective antiarrhythmic prodrug with a large therapeutic index, mimicking lidocaine's benefit without adversity.

Journal article

Wang BX, Nicastro L, Couch L, Kit-Anan W, Downing B, MacLeod KT, Terracciano CMet al., 2022, Extracellular vesicles from human cardiac fibroblasts modulate calcium cycling in human stem cell-derived cardiomyocytes, Cells, Vol: 11, Pages: 1171-1171, ISSN: 2073-4409

Cardiac fibroblasts regulate the development of the adult cardiomyocyte phenotype and cardiac remodeling in disease. We investigate the role that cardiac fibroblasts-secreted extracellular vesicles (EVs) have in the modulation of cardiomyocyte Ca2+ cycling–a fundamental mechanism in cardiomyocyte function universally altered during disease. EVs collected from cultured human cardiac ventricular fibroblasts were purified by centrifugation, ultrafiltration and size-exclusion chromatography. The presence of EVs and EV markers were identified by dot blot analysis and electron microscopy. Fibroblast-conditioned media contains liposomal particles with a characteristic EV phenotype. EV markers CD9, CD63 and CD81 were highly expressed in chromatography fractions that elute earlier (Fractions 1–15), with most soluble contaminating proteins in the later fractions collected (Fractions 16–30). Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were treated with fibroblast-secreted EVs and intracellular Ca2+ transients were analyzed. Fibroblast-secreted EVs abbreviate the Ca2+ transient time to peak and time to 50% decay versus serum-free controls. Thus, EVs from human cardiac fibroblasts represent a novel mediator of human fibroblast-cardiomyocyte interaction, increasing the efficiency of hiPSC-CM Ca2+ handling.

Journal article

Goss C, Culley FJ, Parthasarathy P, MacLeod K, McGregor AH, Sam AHet al., 2022, A paragigm shift in assessment of scientific skills in undergraduate medical education, Advances in Medical Education and Practice, Vol: 13, Pages: 123-127, ISSN: 1179-7258

The General Medical Council’s publication ‘Outcomes for Graduates’ places emphasis on doctors being able to integrate biomedical science, research and scholarship with clinical practice. In response, a new paradigm of assessment was introduced for the intercalated Bachelor of Science program at Imperial College School of Medicine in 2019. This innovative approach involves authentic “active learning” assessments analogous to tasks encountered in a research environment and intends to test a wider range of applied scientific skills than traditional examinations. Written assessments include a “Letter to the Editor”, scientific abstract, and production of a lay summary. A clinical case study titled “Science in Context” presents a real or virtual patient, with evaluation of current and emerging evidence within that field. Another assessment emulates the academic publishing process: groups submit a literature review and engage in reciprocal peer review of another group’s work. A rebuttal letter accompanies the final submission, detailing how feedback was addressed. Scientific presentation skills are developed through tasks including a research proposal pitch, discussion of therapies or diagnostics, or review of a paper. A data management assignment develops skills in hypothesis generation, performing analysis, and drawing conclusions. Finally, students conduct an original research project which is assessed via a written report in the format of a research paper and an oral presentation involving critical analysis of their project. We aspire to train clinicians who apply scientific principles to critique the evidence base of medical practice and possess the skillset to conduct high-quality research underpinned by the principles of best clinical and academic practice. Assessment drives learning, and active learning has been demonstrated to enhance academic performance and reduce attainment gaps in science education.

Journal article

Francis AJ, Firth JM, Gorelik J, MacLeod KTet al., 2021, Activation of GPER limits adverse changes to Ca2+signalling and arrhythmogenic activity in cardiomyocytes of ovariectomised guinea pigs, Publisher: OXFORD UNIV PRESS, Pages: 3208-3208, ISSN: 0195-668X

Conference paper

Dvinskikh L, Harding S, Sparks H, Gorelik J, MacLeod K, Dunsby Cet al., 2021, High speed imaging of calcium dynamics in cardiomyocytes with a flexible light-sheet fluorescence microscope, Biophotonics Congress 2021

Conference paper

Zahra SA, Francis A, Macleod K, 2021, Is GPER-1 involved in post-menopausal cardiac arrhythmias?, 2000 Meeting of the British-Pharmacological-Society (PHARMACOLOGY), Publisher: WILEY, Pages: 423-424, ISSN: 0007-1188

Conference paper

Francis AJ, Firth JM, Islam N, Gorelik J, MacLeod KTet al., 2020, The effect of oestrogen withdrawal on cardiac Ca2+regulation and the influence of GPER1, European-Society-of-Cardiology (ESC) Congress, Publisher: OXFORD UNIV PRESS, Pages: 3599-3599, ISSN: 0195-668X

Conference paper

Firth J, Yang H-Y, Francis A, Islam N, MacLeod Ket al., 2020, The effect of estrogen on intracellular Ca2+ and Na+ regulation in heart failure, JACC: Basic to Translational Science, Vol: 5, Pages: 901-912, ISSN: 2452-302X

Background: Under-representation of women in heart failure (HF) trials and contradictory findings of estrogen supplementation highlight the need to investigate the involvement of estrogen in the progression of heart failure.Objectives: To characterize the influence of estrogen on cardiac function during the onset of heart failure in a controlled animal model that lacks traditional comorbidities.Methods: HF was induced by aortic constriction (AC) in female guinea pigs. Selected AC animals were ovariectomized (ACOV) and a group of these received 17β-estradiol (ACOV+E) supplementation. 150 days post-AC surgery, left ventricular myocytes were isolated and their electrophysiology and Ca2+ and Na+ regulation examined.Results: ACOV animals heart weight/body weight ratios increased by 11% and in vivo fractional shortening decreased by 14% compared with the AC group, suggesting greater impairment of cardiac function in the absence of estrogen. Action potential duration increased in all three HF groups, the extent of the changes being estrogen-dependent. Myocytes from ACOV animals had reduced Ca2+ transient amplitudes, slower transient decay kinetics, decreased SR Ca2+ contents but increased Ca2+ spark frequencies and spark-mediated SR leak compared with the AC and ACOV+E groups. The Na+/K+ ATPase current densities and Na+ extrusion rates were reduced by 13% and 19%, respectively, in parallel with a 17% increase in INa,L current densities in the ACOV group compared with the AC group. Conclusions: Long-term absence of ovarian hormones exacerbates the decline in cardiac function during the progression to HF. Estrogen supplementation reverses these aggravating effects.

Journal article

Lyon A, Babalis D, Morley-Smith AC, Hedger M, Suarez Barrientos A, Foldes G, Couch LS, Chowdhury RA, Tzortzis KN, Peters NS, Rog-Zielinska EA, Yang YH, Welch S, Bowles CT, Rahman Haley S, Bell AR, Rice A, Sasikaran T, Johnson NA, Falaschetti E, Parameshwar J, Lewis C, Tsui S, Simon A, Pepper J, Rudy JJ, Zsebo KM, MacLeod KT, Terracciano CM, Hajjar RJ, Banner N, Harding SEet al., 2020, Investigation of the safety and feasibility of AAV1/SERCA2a gene transfer in patients with chronic heart failure supported with a left ventricular assist device – the SERCA-LVAD TRIAL, Gene Therapy, Vol: 27, Pages: 579-590, ISSN: 0969-7128

The SERCA-LVAD trial was a phase 2a trial assessing the safety and feasibility of delivering an adeno-associated vector 1 carrying the cardiac isoform of the sarcoplasmic reticulum calcium ATPase (AAV1/SERCA2a) to adult chronic heart failure patients implanted with a left ventricular assist device. Enrolled subjects were randomised to receive a single intracoronary infusion of 1x1013 DNase-resistant AAV1/SERCA2a particles or a placebo solution in a double-blinded design, stratified by presence of neutralising antibodies to AAV. Elective endomyocardial biopsy was performed at 6 months unless the subject had undergone cardiac transplantation, with myocardial samples assessed for the presence of exogenous viral DNA from the treatment vector. Safety assessments including ELISPOT were serially performed. Although designed as a 24 subject trial, recruitment was stopped after five subjects had been randomised and received infusion due to the neutral result from the CUPID 2 trial. Here we describe the results from the 5 patients, which confirmed that viral DNA was delivered to the failing human heart in 2 patients receiving gene therapy with vector detectable at follow up endomyocardial biopsy or cardiac transplantation. Absolute levels of detectable transgene DNA were low, and no functional benefit was observed. There were no safety concerns in this small cohort. This trial identified some of the challenges of performing gene therapy trials in this LVAD patient cohort, which may help guide future trial design.

Journal article

Wright P, Tsui S, Francis A, MacLeod K, Marston Set al., 2020, Approaches to high-throughput analysis of cardiomyocyte contractility, Frontiers in Physiology, Vol: 11, ISSN: 1664-042X

The measurement of the contractile behavior of single cardiomyocytes has made a significant contribution to our understanding of the physiologyand pathophysiology of the myocardium. However, the isolation of cardiomyocytes introducesvarious technical and statistical issues. Traditional video and fluorescence microscopy techniques based around conventional microscopy systems result in low throughput experimental studies, in which single cells are studied over the course of a pharmacologicalor physiologicalintervention. We describe a new approach to these experiments made possible with a new piece of instrumentation, the CytoCypher High-Throughput System (CC-19HTS).Wecan assess the shortening of sarcomeres, cell length, Ca2+handling and cellular morphology of almost 4 cells perminute. Thisincrease in productivity means that batch-to-batch variation can be identified as a major source of variability. The speed of acquisition means that sufficientnumbers of cells in each preparation can be assessed for multiple conditions reducingthese batch effects. We demonstrate the different temporal scales over which the CC-HTS can acquire data. We use statistical analysis methods thatcompensate for the hierarchical effects of clustering withinheart preparations anddemonstrate asignificant false positive rate which is potentially present in conventional studies. We demonstrate a more stringent way toperform these tests. The baseline morphological and functional characteristics of rat, mouse, guinea pig and human cells are explored. Finally, we show data from concentration response experiments revealing the usefulnessof the CC-HTSin suchstudies. We specifically focus on the effects of agents thatdirectly or indirectly affect the activity of the motor proteins involved in the production of cardiomyocyte contraction. A variety of myocardial preparations with differing levels of complexity are in use (e.g. isolated muscl

Journal article

Sparks H, Dvinskikh L, Firth J, Francis A, Harding S, Paterson C, MacLeod K, Dunsby Cet al., 2020, Development a flexible light-sheet fluorescence microscope for high-speed 3D imaging of calcium dynamics and 3D imaging of cellular microstructure, Journal of Biophotonics, Vol: 13, ISSN: 1864-063X

We report a flexible light‐sheet fluorescence microscope (LSFM) designed for studying dynamic events in cardiac tissue at high speed in 3D and the correlation of these events to cell microstructure. The system employs two illumination‐detection modes: the first uses angle‐dithering of a Gaussian light sheet combined with remote refocusing of the detection plane for video‐rate volumetric imaging; the second combines digitally‐scanned light‐sheet illumination with an axially‐swept light‐sheet waist and stage‐scanned acquisition for improved axial resolution compared to the first mode. We present a characterisation of the spatial resolution of the system in both modes. The first illumination‐detection mode achieves dual spectral‐channel imaging at 25 volumes per second with 1024 × 200 × 50 voxel volumes and is demonstrated by time‐lapse imaging of calcium dynamics in a live cardiomyocyte. The second illumination‐detection mode is demonstrated through the acquisition of a higher spatial resolution structural map of the t‐tubule network in a fixed cardiomyocyte cell.

Journal article

Ke H-Y, Yang H-S, Francis AJ, Collins TP, Surendran H, Alvarez-Laviada A, Firth JM, MacLeod KTet al., 2020, Changes in cellular Ca2+ and Na+ regulation during the progression towards heart failure in the guinea pig, The Journal of Physiology, Vol: 598, Pages: 1339-1359, ISSN: 0022-3751

We followed changes in cardiac myocyte Ca2+ and Na+ regulation from the formation of compensated hypertrophy (CH) until signs of heart failure (HF) are apparent using a trans‐aortic pressure overload (TAC) model. In this model, in vivo fractional shortening (FS) remained constant despite HW:BW ratio increasing by 39% (CH) until HF developed 150 days post‐TAC when FS decreased from 70% to 39%. Using live and fixed fluorescence imaging and electrophysiological techniques, we found an increase in INa,late from –0.34 to –0.59 A F−1 and a decrease in Na+,K+‐ATPase current from 1.09 A F−1 to 0.54 A F−1 during CH. These changes persisted as HF developed (INa,late increased to –0.82 A F−1 and Na+,K+‐ATPase current decreased to 0.51 A F−1). Sarcoplasmic reticulum (SR) Ca2+ content increased during CH then decreased in HF (from 32 to 15 μm l−1) potentially supporting the maintenance of FS in the whole heart and Ca2+ transients in single myocytes during the former stage. We showed using glycoside blockade in healthy myocytes that increases in SR Ca2+ content and Ca2+ transients can be driven by the same amount of inhibition of the Na+,K+‐ATPase as measured in the diseased cells. SERCA function remains constant in CH but decreases (τ for SERCA‐mediated Ca2+ removal changed from 6.3 to 3.0 s−1) in HF. In HF there was an increase in spark frequency and spark‐mediated Ca2+ leak. We suggest an increase in INa,late and a decrease in Na+,K+‐ATPase current and function alters the balance of Ca2+ flux mediated by the Na+/Ca2+ exchange that limits early contractile impairment.

Journal article

Francis AJ, Firth JM, Islam N, Gorelik J, Macleod KTet al., 2020, The Effect of Oestrogen Withdrawal on Ca<SUP>2+</SUP> Regulation and the Influence of GPER1, 64th Annual Meeting of the Biophysical-Society, Publisher: CELL PRESS, Pages: 403A-404A, ISSN: 0006-3495

Conference paper

Wang BX, Kit-Anan W, Whittaker T, Couch L, Deidda G, Nicastro L, Nagelkerke A, Mitraki A, Harding S, Stevens M, MacLeod K, Terracciano Cet al., 2019, Regulation of cardiac excitation-contraction coupling by human cardiac fibroblasts in health and disease, British-Pharmacology-Society Meeting (Pharmacology), Publisher: WILEY, Pages: 3034-3035, ISSN: 0007-1188

Conference paper

Wang BX, Kit-Anan W, Whittaker T, Couch L, Nagelkerke A, Deidda G, Mitraki A, Harding SE, Stevens MM, MacLeod KT, Terracciano CMet al., 2019, Human Cardiac Fibroblast-Secreted Exosomes Improve Efficiency of Human Cardiomyocyte Calcium Cycling, Publisher: SPRINGER, Pages: 269-269, ISSN: 0920-3206

Conference paper

Thong E, Ahmed A, MacLeod KT, 2019, An Introduction to the Cardiac Action Potentials, HEART OF THE MATTER: KEY CONCEPTS IN CARDIOVASCULAR SCIENCE, Editors: Terracciano, Guymer, Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 49-59, ISBN: 978-3-030-24218-3

Book chapter

Wang BX, Couch L, Kit-Anan W, Whittaker T, Nagelkerke A, Deidda G, Mitraki A, Harding SE, Stevens MM, MacLeod KT, Terracciano CMet al., 2018, Extracellular Vesicles From Human Cardiac Fibroblasts Increase Sarcoplasmic Reticulum-Dependency of Human Induced Pluripotent Stem Cell-Derived Cardiomyocyte Calcium Handling, Publisher: LIPPINCOTT WILLIAMS & WILKINS, ISSN: 0009-7322

Conference paper

Wang B, Deidda G, Mitraki A, MacLeod KT, Terracciano CMet al., 2018, Self-assembling arginine-glycine-aspartic acid-containing peptides abbreviate human cardiomyocyte calcium transients and increase sarcoplasmic reticulum contribution to excitation-contraction coupling, European-Society-of-Cardiology Congress, Publisher: OXFORD UNIV PRESS, Pages: 1209-1209, ISSN: 0195-668X

Conference paper

Firth JM, Yang H-Y, Francis A, Alvarez-Laviada A, MacLeod Ket al., 2018, The effect of oestrogen on Ca2+ and Na+ regulation in heart failure, Biophysical Journal, Vol: 114, Pages: 617a-617a, ISSN: 0006-3495

Journal article

Firth JM, Yang H-Y, Francis AJ, Alvarez-Laviada A, MacLeod KTet al., 2018, The effect of oestrogen on Ca2+ and Na+ regulation in heart failure, 62nd Annual Meeting of the Biophysical-Society, Publisher: Biophysical Society, Pages: 617A-617A, ISSN: 0006-3495

In this work, we show that long-term absence of oestrogen impairs cardiac function and produces detrimental changes to Ca2+ and Na+ regulation in cardiomyocytes following pressure-overload heart failure (HF). Oestrogen supplementation reverses the negative effects of ovariectomy following HF.Pressure-overload HF was induced by aortic constriction (AC) in female guinea pigs. To examine the effects of long-term absence of oestrogen on HF progression, selected ovariectomy (OV) animals underwent AC (ACOV). Pellets containing 17β-oestradiol (1mg, 60-day release) were placed subcutaneously in selected ACOV animals (ACOV+E). Electrophysiological and fluorescence techniques were used to assess Ca2+ and Na+ regulation 150 days post-operatively.ACOV animals heart weight/body weight ratios increased by 11% and in vivo fractional shortening decreased by 14% compared with the AC group, suggesting greater impairment of cardiac function following pressure-overload in the absence of oestrogen. Action potential duration increased in all three interventions but the changes were oestrogen-independent. While ICa and fractional SR Ca2+ release were unaltered, myocytes from ACOV animals typically had reduced Ca2+ transient amplitudes, slower transient decay kinetics, decreased SR Ca2+ contents and increased Ca2+ spark frequencies and spark mediated SR Ca2+ leak compared with the AC and ACOV+E groups. The Na+/K+ ATPase current densities and Na+ extrusion rates were reduced by 13% and 19%, respectively, in parallel with a 17% increased INa,L current densities following ACOV compared with the AC group. Interestingly, myocytes isolated from ACOV animals supplemented with 17β-oestradiol (ACOV+E) typically had similar Ca2+ and Na+ regulation compared with the gonad-intact AC group.Here we present that long-term deprivation of oestrogen, in an animal model whose electrophysiological and hormonal status is akin to human, exacerbates the detrimental effects of pressure-overload HF. Oest

Conference paper

Wang BX, Couch L, MacLeod KT, Harding SE, Terracciano CMet al., 2017, Extracellular Vesicles Secreted From Human Fibroblasts Modulate Human Induced Pluripotent Stem Cell- Cardiomyocyte Calcium Cycling, Scientific Sessions of the American-Heart-Association / Resuscitation Science Symposium, Publisher: LIPPINCOTT WILLIAMS & WILKINS, ISSN: 0009-7322

Conference paper

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